Researchers offered updates on products proven to help against the devastating citrus disease HLB in a virtual seminar on April 27. University of Florida Institute of Food and Agricultural Sciences horticulturists Tripti Vashisth and Fernando Alferez discussed the benefits of gibberellic acid (GA) and brassinosteroids, respectively.
Vashisth reported that GA-treated Valencia orange trees dropped less fruit and increased fruit yields compared to trees in an untreated control during a 2016–22 trial. Five-year average annual production was 2.4 boxes per GA-treated tree versus 1.9 boxes per tree in the control plot. In a 150-tree-per-acre block, that extrapolates to 360 boxes per acre for the GA-treated trees compared to 285 boxes per acre for the control.
An economic analysis indicated that the GA treatments were worthwhile economically. Trees treated with GA reportedly offered a yearly average “profit differential” ranging from $452 per acre to $1,712 per acre when compared to untreated trees.
GA treatments also resulted in more vegetative growth, larger fruit and overall improvements in tree health, Vashisth said.
Vashisth offered some precautions regarding the use of GA. She noted that GA slows the fruit’s color change process or can even reverse color change. GA also suppresses flowering, she said. “Applying too close to bloom could negatively affect bloom/fruit set,” stated a slide in her presentation. “Do not apply after Jan. 10, possibly Dec. 31 … If early flowering is predicted, stop sooner than January.”
In another trial, the use of GA plus 2,4-D reduced preharvest fruit drop by 18%, Vashisth reported. Fruit size also improved in the GA plus 2,4-D trial.
Alferez told seminar participants that most newly planted trees in Florida test positive for HLB within six months. But the use of brassinosteroids reduced the rate of HLB infection after six months to only 25%, he said. He added that researchers don’t know how long that protective effect against HLB lasts.
Brassinosteroids can also advance internal fruit maturation, Alferez reported. Brassinosteroids are a class of growth-promoting steroidal phytohormones.
More than 130 people tuned in to the Vashisth and Alferez presentations.
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